IMO TPMS are of little value when it comes to temperature warning for tires. Same for IR guns.
The question is: How do I make the test both fair and useful? For the pressure test, I decided to eliminate as many variables as possible and get all 12 readings from the same air chamber at the same time and compare them all against my personal digital hand gauge that I have checked against an ISO certified laboratory gauge.
Note: my hand gauge reads to 0.5 psi which is way more precise than anyone needs for checking tires in normal highway use.
Here is the test fixture I made.
Here are the results of my comparison test. The target pressure is 80.0 psi as reported by my handheld digital gauge.
Set A 1 reading of 78 psi, 5 readings of 79 psi
Set B 2 readings of 78, 2 readings of 79 and 2 readings of 80 psi
I also recorded the temperature.
Set A 4 readings of 66 F, one each of 64 and 68F
Set B 4 readings of 69 F and 2 readings of 68
I have recorded the internal vs external pressure difference in reported running pressure with the following results.
I do not consider any of the differences in the readings of the internal vs external sensors pressure to be significant or meaningful for a TPMS, remembering that at Ambient I observed 3 to 5 psi differences when all 12 sensors were measuring an identical pressure, which is not too far off the claimed accuracy for TPMS.